The present invention relates to a membrane magnetic separating apparatus for water purification, solid-liquid separation or the like, and in particular, to a membrane magnetic separating apparatus for continuously performing capturing of a magnetic substance by a membrane and magnetically separating of the captured substance.
A purifying apparatus for the purpose of water purification or the like through solid-liquid separation and using a fine gauze or a net knitted out of polymer fibers as a water separating film to separate and remove particles is described, for example, in xe2x80x9cService Water and Waste Waterxe2x80x9d Vol. 23, No. 9 (1981), pp. 43-52. Such a purifying apparatus comprises a net formed of thin stainless steel wires, polyester fibers, or the like so as to have sieve openings of, for example, several tens of micron meters size so that water to be treated passes through the openings. If a substance to be treated (for example, a contaminant such as water-bloom or an organism) in the water to be treated has a projected area (or a projected diameter) larger than that of the opening in the net, it cannot pass through the net and will be captured and separated from the water, so that the water, permeating through the membrane (net), is purified. When the water to be treated is allowed to continuously permeate the same membrane surface, the substance to be treated deposits on a permeation-side surface of the membrane to increase permeation resistance to extremely reduce an amount of water permeating. Thus, the membrane surface with the deposits (a portion of the surface the membrane below a level of the water to be treated) is moved to an atmospheric portion above the level of the water to be treated, where the membrane is washed using, for example, a shower of purified water. A mixture of the washing water and the deposits is ejected from a separation system as sludge, and the washed membrane surface is returned below the level of the water to be treated.
Alternatively, if a fine contaminant smaller than the projected area (projected diameter) of the opening is to be separated, a coagulant such as aluminum sulfate, polyaluminum chloride, or polyiron sulfate is added to the water to be treated, which is then agitated. As a result, fine solid suspensions, algae, fungi, microorganisms, or the like in the water to be treated are coagulated to a size on the order of several hundred micron meters to form flocs. Forming such flocs enables even a membrane with sieve openings of several tens of micron meters size to capture and separate the fine contaminant at a high removal rate to obtain high quality purified water. A membrane washing structure in this case is the same as the one described above. The sludge is finally transported by a truck to a disposal or incineration field or composted.
In the above conventional examples, the deposits on the membrane surface have a high deposition density (only a small amount of water is contained in the gap among the deposits) and the water content is low. A large amount of washing water, however, is used to remove the deposits from the membrane to reduce the concentration of the deposits (sludge), thereby increasing the water content substantially above that during deposition on the membrane surface.
The water content thereof must be reduced before transportation or compost treatment. It must be reduced to about 85% so as to prevent water from leaking from the sludge when the sludge is transported by the truck to the disposal or incineration field. It must be reduced to about 75% so as to activate micro-organisms that decompose organisms during compost treatment when the sludge is composted. However, the water content of the sludge after washing by water is 99% and the volume thereof thus becomes 15 times (in case of transportation) or 25 times (in case of compost treatment) as large as that before the washing treatment. Since this differential in the water content must be removed, the sludge is further dehydrated using a dehydration means such as a centrifugal dehydrator or a belt press machine. The larger the water content of the sludge in an input section of the dehydration means is, the higher treatment performance the dehydration means must provide, thereby increasing apparatus costs and operation energy costs.
In addition, 5% to 10% of the purified water free from the contaminant is used to wash and remove the deposits collected on the membrane, so that an amount of purified water obtained decreases correspondingly, resulting in a reduced purification capacity.
It is an object of the present invention to provide a membrane magnetic separating apparatus that can separate a substance to be removed captured on a membrane using no or a reduced amount of washing water.
It is another object of the present invention to provide a membrane magnetic separating apparatus that can eject a dense sludge of a substance to be removed of a low water content.
To attain these objects, a first characerizing feature of the present invention is a membrane magnetic separating apparatus comprising: a filter (for example, a net-like body or a membrane-like body) for filtering water to be treated containing magnetic substance to be removed, the filter having sieve openings through which the magnetic substance in the water to be treated cannot pass; a magnetic field generator (for example, a permanent magnet) for magnetically releasing the magnetic substance deposited on the filter from a surface of the filter; a capturing and moving body (for example, a thin shell of stainless steel), provided between the filter and the magnetic field generator, for capturing the magnetic substance released from the surface of the filter while the magnetic substance is spatially moving toward the magnetic field generator, the capturing and moving body further moving the captured magnetic substance from a first space where a magnetic field intensity from the magnetic field generator is high to a second space where the magnetic field intensity is low; a scraper (for example, a spatula) for scraping the magnetic substance captured on the capturing and moving body in the second space; and a sludge vessel for recovering the scraped magnetic substance.
The magnetic substance to be removed may be magnetic floc obtained by adding a magnetic substance and a coagulant or an additive that chemically reacts to the substance to be removed to generate a magnetic substance, to a fluid containing a magnetic or non-magnetic substance to be removed. Furthermore, the substance to be removed may be magnetic floc obtained by adding a magnetic substance to a fluid containing a non-magnetic substance to be removed.
A second characterizing feature of the present invention is a membrane magnetic separating apparatus comprising: a device for generating water to be treated containing a magnetic floc which is formed from a substance to be removed by adding a magnetic substance and a coagulant to a fluid containing the substance to be removed; a filter for filtering the water to be treated, the filter having sieve openings through which the magnetic flock in the water to be treated cannot pass; a magnetic field generator for magnetically releasing the magnetic floc deposited on said filter, from a surface of the filter; a capturing and moving body, provided between said filter and said magnetic field generator, for capturing the magnetic floc magnetically released from the surface of the filter while the magnetic floc is spatially moving toward said magnetic field generator, the capturing and moving body further moving said captured magnetic floc from a first space where a magnetic field intensity from the magnetic field generator is high to a second space where the magnetic field intensity is low; a scraper for scraping the magnetic floc on said capturing and moving body in the second space; and a sludge vessel for recovering the scraped magnetic floc.
It is preferable that the capturing and moving body comprises a water absorbing material having a water absorbing function and means for dehydrating water absorbed by the water absorbing material.
A third characterizing feature of the present invention is a membrane magnetic separating apparatus comprising: a filter for filtering water to be treated containing magnetic substance to be removed, the filter having sieve openings through which the magnetic substance cannot pass; a releasing device for using a force of a fluid such as water or air to release the magnetic substance deposited on the filter, from a surface of the filter; a magnetic field generator for moving the released magnetic substance so as to be magnetically attracted; a capturing and moving body, provided between said filter and said magnetic field generator, for capturing the magnetic substance released from the surface of the filter while the magnetic substance is spatially moving toward said magnetic field generator, the capturing and moving body further moving said captured substance from a first space where a magnetic field intensity from the magnetic field generator is high to a second space where the magnetic field intensity is low; a scraper for scraping the magnetic substance on said capturing and moving body in the second space; and a sludge vessel for recovering the scraped substance.
A heating device may be provided which heats the substance moving on the capturing and moving body. The heating device can be one which selectively heats a dielectric in the substance moving on the capturing and moving body.
A sterilization device may be effectively provided for sterilizing a filtering surface of the filter or a capturing surface of the capturing and moving body.
The capturing and moving body may have an oxidation catalyst for oxidizing organisms on the capturing surface.